Development of an Ultrasound Device for Characterizing Soft Materials and Investigation of Thickness and Force Effects on Peak Density Results

This thesis is focused on developing a reliable and repeatable experimental apparatus to utilize quantitative ultrasound in characterizing soft materials. A specialized device was designed to record ultrasound waveforms in pitch-catch mode while precisely measuring force applied and sample thickness. The design approach initiated with a handheld apparatus which was inadequately constrained for repeatable measurements. The design approach was then changed to a fixed tabletop apparatus. Different components of the device were 3D printed including housings for a load cell and linear rheostat displacement sensor. Two high frequency ultrasound sensors with a nominal frequency of 20 MHz were used. A pulse generator was used to generate a pulse and the transmitted waveform was collected. Fast Fourier Transform was used to convert the waveforms into the frequency domain and an algorithm was used to count the number of peaks and valleys of the waveforms in the frequency domain. This apparatus is then used to measure the peak density on soft tissue phantoms and phantoms containing hard particles such as ground pepper and pepper flakes. An experiment is designed where the phantoms’ thickness and the force applied on the phantoms were varied systematically to evaluate the impact of these parameters on the frequency response. The results revealed a negative effect from increasing the sample thickness on peak density for both homogeneous and ground pepper inclusion tissue phantoms. However, no significant effect was observed for tissue phantoms with pepper flake inclusions. Correlation analyses between applied force and peak density showed mixed results, with significant correlations found for non-homogeneous tissue phantoms but not for homogeneous samples. For the non-homogeneous tissue phantoms, the peak density increased with increasing force for tissue phantoms with ground pepper inclusions and decreased with increasing force for tissue phantoms with pepper flake inclusions. These findings suggest a complex relationship between sample thickness, inclusions, applied force, and resulting peak density. Understanding these relationships is crucial for accurate ultrasound-based tissue characterization and highlights the need for further research in this area. Future work is suggested, including testing with real tissue samples and automating the device for faster measurements and analysis.